//part1:C09:ex9.24.cpp
#include <iostream>
#include <vector>
using namespace std;

int main(void) {
  vector<int> iv;
  cout << iv.at(0) << endl;
  cout << iv[0] << endl;
  cout << iv.front() << endl;
  cout << *(iv.begin()) << endl;

  return 0;
}
